fix(router): let type checkers see the real Router constructor arguments (#50278)

litellm/proxy/management_endpoints/router_settings_endpoints.py

@@ -68,7 +68,7 @@ def _get_routing_strategies_from_router_class() -> list[str]:
     Dynamically extract routing strategies from the Router class __init__ method.
     """
     # Get the __init__ signature
-    sig: Final = inspect.signature(Router.__init__)
+    sig: Final = inspect.signature(Router)
 
     # Get the routing_strategy parameter
     routing_strategy_param: Final = sig.parameters.get("routing_strategy")

litellm/router.py

@@ -52,7 +52,7 @@ if TYPE_CHECKING:
 # ``Router(...)``'s parameters, their defaults and its docstring: ``router_arguments`` binds a call
 # against them and ``Router.__init__`` reports them. The body is never run.
 def _router_init(
-    self,
+    self: object,
     model_list: list[DeploymentTypedDict] | list[dict[str, Any]] | None = None,
     ## ASSISTANTS API ##
     assistants_config: AssistantsTypedDict | None = None,
@@ -222,17 +222,22 @@ def _class_descriptor(cls: type, name: str) -> bool:
 
 
 if TYPE_CHECKING:
-    from typing import overload
+    from typing import ParamSpec, overload
 
     from litellm.litellm_core_utils.streaming_handler import CustomStreamWrapper
     from litellm.types.llms.openai import AllMessageValues, OpenAIFileObject
     from litellm.types.utils import EmbeddingResponse, LiteLLMBatch, ModelResponse
 
+    _P: Final = ParamSpec("_P")
+
+    def _takes_parameters_of(source: Callable[_P, None]) -> Callable[[Callable[..., None]], Callable[_P, None]]: ...
+
     class Router(RustCore, DeprecatedRouterMembers):
         """What type checkers see: the constructor's parameters and the endpoints' return types. The
         endpoints are served by the core at run time (litellm/router_rust/invoke/endpoints.py)."""
 
-        __init__ = _router_init  # pyright: ignore[reportAssignmentType, reportIncompatibleMethodOverride]  # Router(...)'s parameters
+        @_takes_parameters_of(_router_init)
+        def __init__(self) -> None: ...  # pyright: ignore[reportMissingSuperCall]  # a type-checking stub
 
         @classmethod
         def from_config(cls, config: RouterConfig, host: PythonHost = python_host) -> "Router": ...

litellm/router_utils/handle_error.py

@@ -26,7 +26,7 @@ async def send_llm_exception_alert(
     ctx: "RoutingContext | None",
     request_kwargs: dict,
     error_traceback_str: str,
-    original_exception,
+    original_exception: Exception,
 ):
     """
     Only runs if router.slack_alerting_logger is set
@@ -34,7 +34,7 @@ async def send_llm_exception_alert(
 
     Parameters:
         ctx (RoutingContext): The router's routing context.
-        original_exception (Any): The original exception that occurred.
+        original_exception (Exception): The original exception that occurred.
 
     Returns:
         None